Our lab is focused on understanding the role of macrophage dysfunction in the pathogenesis of diabetes complications such as poor wound healing, infections, and heart failure. A hallmark of diabetes and obesity is the accumulation of lipids in non-adipose tissues. In the case of macrophages, the diabetic milieu leads to increased saturated fatty acid (SFA) content and in particular palmitate. To investigate how dietary fatty acids in the microenvironment can alter macrophage biology during inflammation we developed an ex vivo system in which primary macrophages are incubated with the SFA palmitate and then activated with the toll like receptor 4 (TLR4) ligand LPS. Using this experimental system we discovered that crosstalk between these nutrient and inflammatory signals leads to lysosome damage and dysfunction. This pathway is independent of MAP kinases and NF-kB, but requires the alternate TLR4 adaptor TRIF. As a consequence of lysosome pathology macrophages undergo a unique form of caspase-independent cell death and activate an inflammatory complex known as the inflammasome. We are interested in dissecting the pathways that converge on the lysosome to produce macrophage pathology and assessing the physiologic relevance of these events in animal models of diabetes complications.
Molecular Mechanisms of Lipid Toxicity in Macrophages
In order to understand how TLR activation in FA-rich environments produces lysosome dysfunction we have focused on two major questions:
- How is macrophage metabolism is reprogrammed during activation and how this is altered by the presence of FFAs?
- What are the pathways downstream of TLR4 and TRIF that combine with FA to mediate toxicity?
To achieve these aims we are utilizing a combination of myeloid specific gene knockouts, macrophage function assays (cytokine release, phagocytosis, survival), cell metabolism assays (Seahorse), and metabolomics approaches. The main objective of this line of research is to identify metabolic pathways in macrophages that could serve as therapeutic targets for diabetes complications and other inflammatory disorders.
Disease Models of Metabolic Complications
Diabetes impairs the body’s response to tissue damage and/or infection and macrophage dysfunction is a likely contributor this phenotype. Clinically relevant manifestations of this phenomenon include poor skin wound healing after injury, increased frequency and severity of urinary tract infections, and heart failure following myocardial infarction or inflammatory injury. To investigate these complications at a cellular and molecular level we have models of skin, cardiac, and infectious injury that we have combined with high-fat diet induced metabolic stress. These in vivo systems are being used to translate molecular findings from our ex vivo work using myeloid specific knockout approaches.